(a) Field of the Invention
This invention relates to a system for providing remote hydrojet borehole mining, and more specifically, but not by way of limitation, to a hydraulic borehole mining system with interchangeable components that allow the use of a single device for a plurality of tasks. Some of the tasks that the instant invention could be used for: extraction or the mining of a mineral resources; the creation of a subsurface cavity or void space; to stimulate liquid and/or gas production; clean lake bottoms; recover either liquid or solid environmental contaminates; or other related uses which require a remotely operated tool.
The Borehole Mining Tool (tool) is intended for mining of mineral resources, through boreholes. This tool may be applied from the Earth""s surface, underground mines and ocean platforms. The tool also will find an application in geological exploration for bulk sampling, in building of subterranean storages, in-situ leaching, production stimulation for oil/gas and water, in custom foundations, underground collectors construction, environmental clean up of subterranean spills and more. The tool can be used to solve other environmental problems, such as cleaning of lake bottoms and removing ooze, cleaning of oil reservoirs, radioactive contamination (nuclear missile silos), and other applications requiring remote operating.
(b) Discussion of Known Art
Borehole mining (BHM) as a remote underground mining method is based on water jet cutting of rock material. This is accomplished by pumping high pressure water down to the working area from the Earth""s surface (or underground mines, or floating platforms) to the borehole mining tools lowered into pre-drilled holes. The slurry created by the water jet is simultaneously pumped out by the same tool. By removing the broken materials, underground cavities (stopes) can be created.
The BHM approach has many recognized advantages, but the method has not gained acceptance commensurate with its potential due to several important issues that have yet to be finalized. One of the most significant problems has been the specialized tooling needed for mining of different type of material and specific geo-technical and environmental tasks to be performed, which requires that the user needs to carry and the use of different tools to the work site instead of a universal one. These tools are typically large and heavy units having a minimum number of joints, couplings, threads and other easy-and-quick connectors which complicates the tool""s assembly, accessibility, serviceability and replacement. In case of a failure of some part of the tool, the replacement of this disabled unit(s) usually requires a replacement of most, if not all, of the tool.
Another problem is that borehole mining is a blind method; there is no data about the current cutting direction as well as the current configuration of the driving space (cavern/stopes). All geophysical measurements (logging) may be executed only after all operations are stopped and the BHM tool is removed from the hole. This typically equates to several hours of down time. Additionally, because borehole mining is carried out in friable, unconsolidated (unstable) material, the shape of the created stopes can be easily changed by collapsed rock masses. Thus, measurements, made after stopping of operation can not always be used for estimation of production. Best downhole measurements must be made while mining: or xe2x80x9clogging-while-miningxe2x80x9d (LWM). This instant tool will allow for the attachment of monitoring devices which will give xe2x80x9ceyesxe2x80x9d to borehole mining.
In certain circumstances it is necessary to build vertical slots using several boreholes and then connecting them to each other, for example to create an extended underground collecting ditch. In this task, information about orientation of the tool""s nozzle down in a borehole becomes very critical. But, through assembling and lowering the tool in a hole, its bottom part (which contains the head and the hydromonitor""s nozzle) is twisted relative to the upper portion of the tool. Thus, after the tool is assembled and lowered down in a hole, there is no further information about the current bottom head""s nozzle orientation; as it is lost while assembling.
In borehole mining, a hole is first drilled from the surface to a depth where the mineral deposit or work area is located. A metal or plastic casing, which is nothing more than a heavy pipe, is then inserted into the hole to prevent sidewall caving or capsizing of the hole. The casing bottom end, called a casing shoe is placed immediately above the future working (production) interval. Then, the borehole mining tool is lowered into this casing until its bottom (working) end portion reaches the xe2x80x9copenxe2x80x9d hole, right bellow the casing shoe.
The BHM tool consists of three main parts: an upper head, an intermediate column and a bottom (working) head. The upper head includes stub-pipes for pumping in a working high-pressure fluid (usually water) and for discharge of production slurry; a swivel; a turn table; and a mechanism for raising/lowering the tool while mining. The intermediate column is comprised of two or more pipes assembled in xe2x80x9cpipe-in-pipexe2x80x9d manner by numerous dual conduit sections. At the end of this column is the bottom head with its hydromonitor and eductor (also known as hydro-elevator, or jet-pump). In most cases, a drill bit can also be placed at the bottom end of the tool.
The inner and outer columns of the tool form an O-shape gap. Thus, the tool has at least two hydraulic channels: one is the inner pipe""s channel (inner channel), and the other is the aforementioned ring gap, or outer channel. These channels are used for delivery of high pressure working fluid (water) to the bottom head and for elevating production slurry back to the surface. It is obvious that two channels are the minimum required in borehole mining. Therefore, in BHM two main schematics of water/slurry circulation are used: (1) the xe2x80x9cdirectxe2x80x9d; water is pumped by inner pipe and slurry is received by the gap and (2) the xe2x80x9creturnxe2x80x9d; opposite circulating. Because of its relative simplicity, over 90% of existing BHM tools are based on these two schematics. The schematic of fluids circulating is reflected on the configuration of the top head and other surface equipment.
The borehole mining tool functions as follows: The tool is lowered into a borehole until the hydromonitor (which is located in a bottom head) is placed below the casing shoe in an open hole to the depth that the actual mining is to take place. Next, the high pressure (working) water, approx 2000 psi at a flow rate of 1000 GPM, is pumped down to the tool through one of the two channels or annulus"" contained in the intermediate pipe. In the bottom head one part of this water is split off to the hydromonitor which contains a nozzle directing the water to the area to be worked-out. As it passes through the nozzle, this flow accelerates to a water jet that is sufficiently powerful to break and scale away the material being mined. The loosened rock/ore material from the worked out area is fluidized through mixing with water to create a productive (pregnant) slurry.
The created slurry must be drawn to the surface to clean the working space (stope/cavern) and to recover the desired mineral(s) or create the desired cavity. For this purpose, the remaining portion of the working water continues flowing down until it reaches the eductor which forces it to turn which creates a vacuum in front of the Venturi pipe opening. This vacuum sucks the incoming slurry, drawing it into the slurry channel of the tool and then it is transported up the pipe until it reaches the surface.
On the surface, the water contained in the slurry is separated from heavy particles (rock/ore chunks and other solids)in a collecting pond or tank by gravity force (and/or other standard equipment, if needed). The clarified water is pumped down to the working interval again. This completes the BHM water re-circulating cycle. While operating, the tool is rotated and moved up and down in the hole within the production (working) interval. The borehole mining process usually creates underground caverns.
It can be appreciated that the effectiveness of the rock cutting and slurry recovery are of great importance in the overall performance of the whole BHM tool and operation. One method of causing the slurry to rise through the return (slurry) channel is by pressurizing the entire system, including the cavity where the mining operations are being carried out, thus forcing the slurry through the return pipe. Another method for drawing the slurry to the surface is to include an eductor near the lowest point on the tool in order to force draw the slurry into the return pipe.
The eductor type pump has been favored in borehole mining since the simplicity of the device results in high reliability. The need for high reliability is a critical element for borehole mining tools, since failure of a component at a great depth can result in long down times and expensive procedures for trying to retrieve the tool through the borehole. The Venturi effect that is used to draw the slurry into an orifice(s) (slurry intake port(s)) in the device is created at a region on the tool that lies below the cutting jet. This allows the tool to draw material from the lowest possible position in the cavity created by the tool. Often, however, the orifice used to draw material is not at the lowest point on the tool. Therefore, with these configurations additional portions of the tool are located at the lowest position within cavity being mined. This is a serious disadvantage since the solids of the slurry will tend to settle and fill this low area.
Examples of tools which include points that are below the slurry intake ports include U.S. Pat. No. 5,366,030 to Pool, U.S. Pat. No. 4,718,728, and 4,296,970 to Hodges, U.S. Pat. No. 4,212,353 to Hall, U.S. Pat. No. 4,140,346 to Barthel, U.S. Pat. No. 4,059,166 to Bunelle, and U.S. Pat. No. 3,747,696 to Winneborg et al. Known devices for borehole mining have suffered from limited applicability. For example, one known device taught in U.S. Pat. No. 5,181,578 to Lawler, is a borehole mining tool which uses a swing-away hydromonitor that collapses to allow extension or retraction of the nozzle. This extension and retraction of the nozzle allows the user to improve the reach of the nozzle within the cavity being mined.
Another device which addresses the problems associated with the reach of the cutting jet nozzle is taught in U.S. Pat. No. 4,915,452 to Dibble. The Dibble invention teaches the use of a cutting head nozzle which can be moved relative to the rest of the tool in order to manipulate the position of the cutting jet without affecting the position of the slurry or intake portion of the tool.
A known device for borehole mining is shown in U.S. Pat. No. 4,934,466 to Paveliev, which has the blast pipe going through the eductor nozzle. With the same rate of pumping water, it allows an increase in the suction of the eductor because the diameter of its nozzle and thus the diameter of the water jet is also increased. This tool is not free from disadvantages. The drill bit located below the eductor does not allow slurry to be recovered from the very lowest points of the working area. Thus, this tool can not be successfully used, for example in cleaning of oil (or any other) storage, vessel or tank. The other disadvantage of this invention is the usage of an external pipe as a slurry channel. It excludes the possibility of using an airlift because there is no simple method to place an air pipe in this gap due to its rotation. Further, the annulus channel has 2 to 3 times smaller cross section than the inner pipe. This limits the maximum possible size of slurry chunks to be transported through the external channel in comparison to the internal one. Finally, these xe2x80x9cdoublexe2x80x9d walls increase the slurry pressure loss nearly two-fold due to the doubled hydraulic friction. In other words, the usage of an inner column as a slurry line, as does the Paveliev tool, increases the maximum size of transported chunks, while decreasing slurry flow pressure loss. The above mentioned disadvantages narrow the area of this tool application.
U.S. Pat. No. 5,366,030 to Pool has a design similar to Paveliev construction and is suffering from the same problems. Additionally, both devices have only two hydraulic channels. In certain circumstances, a tool with three or even four individual channels is required. Also, structurally these two devices are based on using a casing column as an outer pipe of the tool. However, oftentimes, structural and hydro geological conditions of the deposit allow operation in a borehole without the requirement to stabilize the walls through the uses of a casing string. In this situation, a double wall tool is preferable as it saves operational time and capital cost, because the outer pipe is xe2x80x9ctravelingxe2x80x9d together with the tool from hole to hole instead of remaining in each worked-out well.
Another known device for borehole mining is U.S. Pat. No. 4,059,166 to Bunnelle. This device is also based on the xe2x80x9cpipe-in-pipexe2x80x9d double column construction. These two columns define two hydraulic channels: the innerxe2x80x94slurry channel, and a gap between inner and outer columns which is used as high pressure water channel. At the bottom of the tool, there is a working head with a hydromonitor and an eductor sections. This device works as follows: The high pressure water is pumped down through the gap between inner and outer columns. At the hydromonitor section, part of the flow is diverted to the hydromonitor and becomes a water jet directed toward the rock which it cuts. Broken parts of rock material are mixed with spent cutting water to create a pregnant (productive) slurry. Another portion of the working water continues its movement down and finally reaches the eductor which produces the vacuum. This vacuum sucks the coming-up slurry. The slurry enters the inner pipe, through with it reaches the surface. The hydromonitor which has a cylindrical barrel and a standard conical nozzle at its end crosses the inner (slurry) pipe, splits (bifurcates) the flow at that point, forming a slurry fork-pass around the hydromonitor. The eductor section of the Bunnelle tool has a needle in its nozzle. This needle controls the suction of slurry in the same manner as the tools mentioned above. It also has a distribution reservoir located below the eductor. A drill bit can be attached to the reservoir which is located at the lowest point of the tool. In addition to an Earth""s surface application, this tool can be mounted on a sea/ocean platform or barge and used to develop an offshore mineral zone or create voids for foundation or other requirements.
The Bunnelle device has the most relative (closest) design to the instant invention.
Main disadvantages of the Bunnelle tool are following:
1. Limited area of application. The tool can not remove the slurry at the lowest point of the working area because below the suction area is located the distribution reservoir and the drill bit.
2. A high number of moving mechanisms, parts, springs, pistons and cylinders decrease the reliability of the device, while increasing hydraulic friction and water pressure loss.
3. The inlet to the hydromonitor is located very close to the outer pipe wall. Part of the high pressure water flow makes a sharp turn to come into the hydromonitor at this point. The very high velocity of the water flow (5-10 m/sec), along with the sharp turn and the narrow space where this turn occurs, creates a high grade turbulence in water flow right before the hydromonitor nozzle. As a result, it negatively reflects on the hydrodynamic characteristics of the water jet: it becomes an unfocused, spray-type flow. Obviously, it therefore, decreases the water-jet productivity and also decreases the tool""s overall borehole mining effectiveness.
The main disadvantage of all the afore mentioned devices is their limited area of application. Each of these tools was developed for a specific borehole mining task of which it can successfully execute. At the same time, choosing of the type of the borehole mining tool is based on a combination of different types of various criteria such as a deposit""s hydro-geological situation, hardness, specific gravity, granule distribution of the mining material(s), depth of operations, rock mechanic characteristics of cap and bed rocks and several additional criteria. This combination dictates the type and configuration of borehole mining tooling, equipment and methods of BHM operation. Thus, for example, a tool which can effectively develop a sand-type material may not be very successful at the mining a clay-type material. Another example: a device for borehole mining can not be effectively applied for the purpose of cleaning a metal reservoir, and for creating underground pillars. Thus, there still remains the need for a universal borehole mining tool which can be easily modified to suit varied operations and technical tasks.
Borehole mining practice requires that, in some circumstances, it is necessary to have a four channel BHM tool. In addition to (1) water and (2) slurry channels, there is often a need for a channel for (3) air lift and another (4) extra channel for injection of a secondary agent to the working area to improve the effectiveness of the mining or cleaning process. Thus, it is important to have a 4 channel tool.
Another important aspect of the borehole mining tool, is its weight. Borehole mining is typically conducted at depths in excess of 50 m (150 feet) to 200 m (600 feet), and even deeper to 1 Km (3,300 Ft). Since the tool must be rotated at such a great depth while being suspended in a hole, it must be able to support not only its own weight, but also weight of water and slurry columns in both channels and transmit the torque through the tool""s body. As it was shown before, in general, BHM tools have doubled body (xe2x80x9cpipe-in-pipexe2x80x9d) construction, which doubles the weight of the tool and limits the working depth because of the risk of the tool rupture and loss. It also increases the tool initial and operational cost. Thus, it is important to reduce the weight of the tool.
There remains a need for a borehole mining tool which reduces pressure losses while pumping the working water through the bottom head and returning slurry to the surface. Importantly, there remains a need for a borehole mining tool that allows the user to know the orientation of the water jet being delivered to the working area. Still further, there remains a need for a borehole mining tool that allows the user obtain an image of the shape of the excavated area while mining, and thus increase the effectiveness of the jet cutting, raise safety and, finally, improve borehole mining as a process.
It has been discovered that the problems left unsolved by known art can be solved by providing a borehole mining tool with a bottom head with a universal connector that can accept various mechanical components and parts to easily modify the function of the whole device. Thus, a configuration of the tool for a specific task can be carried out by simple modification of the bottom portion, or by replacing of some components by the same-type components with a different technical or hydro-dynamical characteristics as explained below.
Another aspect of the instant invention, is that an improved hydromonitor section for use with the tool has been developed. The hydromonitor includes a conical barrel and a nozzle that is positioned slightly offset from the center area of the hydromonitor section. The offset positioning of the entry of the hydromonitor provides for a more smooth turning of the pressure water flow as it enters the hydromonitor. This decreases the turbulence in the working fluid flow and improves the availability of fluid to the nozzle, thereby, enhancing the water jet characteristics. This makes the jet more focused and thus more powerful. Finally, it increases the tool""s working radius and productivity of the rock cutting and overall borehole mining effectiveness.
The orientation of the hydromonitor nozzle as well as the overall shape of the driving cavity being created in the strata as it is being developed can be obtained by including a radar device near the nozzle of the hydromonitor, along with a current generator to produce small currents and a device to measure current changes as the tool is moved through the Earth""s natural magnetic field. The signals collected from the radar and the current generator can be used to derive the orientation of the nozzle relative to the Earth""s magnetic field (survey) and an image of the cavity formed while mining. Developing this data allows for the creation of a current 3D image of the driving space (cavern) and also for the instant calculation of its volume and the current productivity of the Borehole Mining operation itself.
While the above and other advantages and results of the present invention will become apparent to those skilled in the art from a study of the following detailed description and accompanying drawings, which explain the contemplated novel construction, combinations and elements as herein described, and more particularly defined by the appended claims, it should be understood that changes in the precise embodiments of the herein disclosed invention are meant to be included within the scope of the claims, except insofar as they may be precluded by the prior art.
The main idea and the purpose of this instant invention is the development of a multi functional (universal/versatile) borehole mining tool. By the shifting of various parts, details and units this device changes its functional features which expands the area of its application, enabling it to work in different hydro-geological conditions and physical properties in the extraction of material(s). Additionally, this tool should present higher reliability, less water/slurry pressure loss, lower device total weight and a reduction in the cost of its manufacture and operation. This tool also should be able to solve different type of mining, environmental, building and other problems. In other words, this tool should be universal, with the ability to execute different types of jobs depending on the engineering task requirements by simple shifting of its working parts, details, and units.
To achieve this purpose this tool should have:
wider area of application,
increased reliability,
improved hydrodynamic characteristics of water and slurry channels,
possibility of control of the driving space (cavern),
four individual hydraulic channels,
possibility of decreasing the weight of the device,
lower initial and operational cost.